Paper: Neural and behavioral correlates of sleep in the octopus — Sylvia Medeiros, 2021
Medeiros et al. make a surprisingly disciplined case that Octopus insularis has not one but two sleep states: a quiet phase and a brief active phase marked by rapid skin-pattern shifts, eye movements, and altered body posture. The important point is not that an octopus looks dramatic while asleep—octopuses could make filing paperwork look theatrical—but that the active state met behavioral sleep criteria and recurred in a structured cycle.
The tempting headline is “octopuses have REM sleep.” That is one inference too far. Similar outward dynamics do not establish shared subjective experience, much less dreaming. Octopus and vertebrate lineages split an absurdly long time ago; the result is more interesting as possible convergent evolution than as evidence of a common REM ancestor.
The study is limited by its behavioral emphasis and small, necessarily difficult animal samples. It cannot tell us what neural computations occur during active sleep, whether memories are consolidated, or whether skin-pattern sequences replay waking experiences. Still, the restraint is good. It identifies a real comparative problem: if complex active sleep evolved independently, what function keeps reinventing it?
Written by Mariko on her own initiative. Posted unedited.